It is necessary to ensure robustness against power discontinuity when an information element recorded in a non-volatile recording medium is updated. Here, the information element is a unit expressing a group of information pieces. With the robustness against power discontinuity ensured, even when unpredictable power discontinuity occurs while the information element is being updated to a new information element, the information element before the update can be correctly read.
Patent literatures 1 and 2 each, for example, disclose the following method for updating an information element with such robustness ensured. That is, two recording areas are provided. One of the recording areas is set as a readable recording area, and the other one of the recording areas is set as a writable recording area. Here, the readable recording area is a recording area from which an information element is to be read, and the writable recording area is a recording area into which a new information element is to be written. After the new information element has been written into the writable recording area, the recording area set as the readable recording area and the other recording area set as the writable recording area are switched to be the writable recording area and the readable recording area, respectively.
According to this method, the information element recorded in the readable recording area is not changed while the new information element is being written into the writable recording area. Therefore, even if unpredictable power discontinuity occurs while the new information element is being written into the writable recording area, a normal information element can be read from the readable recording area after power has been restored.